Audio filter for reducing rumble or hiss?

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I am looking for an audio filter to reduce / remove an occasional rumble and
a constant background hiss from a movie. I would like one that I can use
within Movie Maker, but if I cannot find one I could run a clean up on the
finished WMV file.

Does anyone have any ideas?

Thanks in advance,

Dave
 
Dave,
Typically the built in mics in camcorders are notorious for picking up tape
motor noise, and other mechanical vibrations and recording them along with
ambient audio for posterity. Your problem described is sorta 2 fold:
"rumble" is low frequency (theoretically filtered out by a HPF = High Pass
Filter), but "noise" is
either broadband frequencies (wide spectrum) or relatively high freq. band
"hiss",
so a HPF wouldn't block that and any filter that attenuated the bradband
"noise" would most likely also attenuate your "signal" and thus not improve
your S/N ratio. If the "hiss from a movie" was tape hiss from an analog tape
source (e.g. a VHS tape movie) you can not clean it up and make it better
than the source.
Thus GIGO = Garbage In, Garbage Out. Once the signal and noise are combined
on the same audio track(s) they exist as 1 analog sound (or digital data
stream if encoded after the mix).

In case you're wondering, the way the nifty noise cancelling headphones work,
basically it never lets the background noise source get combined with the
program signal audio feed. It does that by collecting the ambient background
"noise" through an external mic or transducer and feeding that audio line
through 2 inputs of a "differential amp" chip, one of which is the reverse
polarized (mirror opposite) of the normal input, and the chips output is the
"difference" of the 2 inputs, which is zero level no noise. That then is
mixed with the true source program audio "signal" and output to the
headphones. So the noise doesn't get into the program audio, only the
preprocessed "zero summed" cancellation signal
gets mixed with the desired audio source.

However, analog tape noise added to the analog playback audio circuitry
noise is an inseparable noisy program.

But the 1 thing you can do, to return to the first HPF aspect, is filter out
the low rumble by inserting some "rumble filter" inline between the noisy
source audio and the input of the recorder/digitizer/whatever. My Mackie
mini mixer has on each of it's mic input channels, a HPF mic rumble cutout
filter button that chops out low ("rumble") frequencies, below about 150 Hz.
If you could find some filtering device like that it would need to accept
LINE LEVEL inputs and output LINE LEVEL to your
recorder/processor/digitizer/whatever, rather than unamplified MIC level
signal, as in my Mackie mixer example.

Good luck!
 
Dave Nuttall said:
I am looking for an audio filter to reduce / remove an occasional rumble
and
a constant background hiss from a movie. I would like one that I can use
within Movie Maker, but if I cannot find one I could run a clean up on the
finished WMV file.

Does anyone have any ideas?

Thanks in advance,

Dave
Click to expand...

Hi
It is a common issue and really no viable solution.
There are filtering utilities but are pricey, and as
knowbuddy has pointed out, to clean up noise that
is within the audioband frequencies will be at the
expense of fidelity.
There is freeware, and a community to guide you at:
http://audacity.sourceforge.net/

The audacity software available to download involves
saving the audio track as a wav file, applying filtering
to specific frequencies, then saving as a new and
filtered wav, but then you will have to sync it back to
the DV-AVI video track, quite a tricky process, especially
if the footage involves individuals and speech etc
I have to add, I have never used this specific software
in this context.
 
Thanks for the pointers guys.

I've tracked down a couple of Audio Editors that may be of use. I'm going to
try using them to pull the audio from the finished movie, clean it up, and
write it back out as a WMA file. I should then be able to put this in the
"music" track of Movie Maker and visually check that everything is still in
sync.

I'll post another reply with my results in a week or so...
 
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